Control of a Vanadium Redox Battery and supercapacitor using a Three-Level Neutral Point Clamped converter A. Etxeberria a, * , I. Vechiu a , S. Baudoin a , H. Camblong a, b , S. Kreckelbergh a a ESTIA, F-64210 Bidart, France b Department of Systems Engineering & Control, University of the Basque Country, (UPV-EHU), Europa Plaza 1, E-20018 Donostia, Spain highlights  The control of a hybrid storage system using a Three-Level NPC converter is analysed.  A Hybrid Energy Storage System formed by a SC and a VRB is used.  A control algorithm is presented to divide the power between a SC and a VRB.  The system is validated in simulations and experimentally in two case studies. article info Article history: Received 3 July 2013 Received in revised form 18 September 2013 Accepted 7 October 2013 Available online 26 October 2013 Keywords: Energy management Energy storage Microgrid Power converters Renewable energy abstract The increasing use of distributed generators, which are mainly based on renewable sources, can create several issues in the operation of the electric grid. The microgrid is being analysed as a solution to the integration in the grid of the renewable sources at a high penetration level in a controlled way. The storage systems play a vital role in order to keep the energy and power balance of the microgrid. Due to the technical limitations of the currently available storage systems, it is necessary to use more than one storage technology to satisfy the requirements of the microgrid application. This work validates in simulations and experimentally the use of a Three-Level Neutral Point Clamped converter to control the power flow of a hybrid storage system formed by a SuperCapacitor and a Va- nadium Redox Battery. The operation of the system is validated in two case studies in the experimental platform installed in ESTIA. The experimental results prove the validity of the proposed system as well as the designed control algorithm. The good agreement among experimental and simulation results also validates the simulation model, that can therefore be used to analyse the operation of the system in different case studies. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction The use of the Renewable Energy Sources (RES) is continuously increasing due to the global climate change, the limitation of the fossil fuels and the social awareness concerning this subject. The energy obtained from the RES has many advantages compared with the conventional sources, but on the other hand it is stochastic and consequently difficult to control. Due to this drawback, a high penetration of the RES can create stability, reliability and power quality problems in the main electrical grid [2,1]. Thus, an optimum way of integrating the energy obtained from the RES must be designed. The microgrid is being analysed as a solution to this problem. A microgrid can be defined as a system that has at least one distrib- uted energy resource, energy storage systems, power conversion systems, control systems and loads [3] (see Fig. 1). Its main char- acteristic is its ability to work not only connected, but also disconnected from the main electrical grid. An Energy Storage System (ESS) is usually necessary in a microgrid to maintain the power and energy balance as well as to ensure a high power quality electricity supply. Nowadays there are many different types of storage technologies [5,4], but unfortu- nately none of them satisfies the requirements of the microgrid application: an ESS must have a high specific power in order to face fast power variations, and at the same time it must have a high specific energy to give autonomy to the microgrid. For that reason, it * Corresponding author. ESTIA-Recherche, Technopole Izarbel, 64210 Bidart, France. Tel.: þ33 05 59 43 85 06; fax: þ33 05 59 43 84 05. E-mail address: a.etxeberria@estia.fr (A. Etxeberria). Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour 0378-7753/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jpowsour.2013.10.021 Journal of Power Sources 248 (2014) 1170e1176